An evaporative air conditioner or cooler typically comprises a box-like enclosure having louvred side walls that are lined with a filter medium. A fan is located within the enclosure for drawing air into the enclosure through the filter medium. The air is then forced by the fan into the space or room to be cooled. The cooling of the air is achieved by evaporation of water as it passes through the filter medium which is kept saturated with water. The filter medium is supplied with water from a sump or reservoir in the base of the enclosure by a recirculation pump.
As water is continuously lost to the atmosphere by evaporation, a water supply line replenishes the reservoir in the base of the enclosure with fresh water. The water level in the reservoir is typically maintained at a constant level by a float valve provided in the water supply line. Over time the recycled water in the reservoir becomes saturated with minerals and salts which results in problems with corrosion and blockages. Furthermore, the water in the reservoir can also be an ideal incubator for bacteria and other micro-organisms. Accordingly, various arrangements have been proposed for preventing this build up of salts and/or for draining the sump or reservoir of water to avoid these problems.
AU 49797/85 (CELI MANUFACTURING PTY. LIMITED) describes a bleed-off valve for an evaporative cooler designed to overcome deficiencies in the use of a prior art bleed-off line and clamping arrangement provided in the fluid line between the recirculation pump and a water distribution point at the top of the enclosure. The bleed-off valve of AU 49797/85 is typically located in the fluid line between the recirculation pump and water distribution point and comprises a gate valve that facilitates manual adjustment of the bleed-off flow rate using a tap-type valve actuating means. Thus the problems with the use of the prior art bleed-off line and clamping arrangement are eliminated. However, the provision of a bleed-off valve does not overcome the problems associated with water retained in the reservoir after the cooler is switched off.
Other prior art arrangements include the provision of a dump valve in the sump or reservoir for draining the water when the cooler is switched off. The prior art dump valves typically include a solenoid operated valve or a flap valve actuated by mechanical linkages that can be manually operated or that operate in conjunction with the float valve to drain the reservoir at regular intervals. A disadvantage of these prior art systems is the increased complexity of the water flow control system with an attendant reduced reliability. A further disadvantage is that such systems tend to waste excessive amounts of water.